Synthetic lube stocks

ABSTRACT

The present invention relates to synthetic lubricant base oil stocks having a low pour point and consisting essentially of an admixture of mono- and dialkyl benzenes, wherein the alkyl substituents are substantially similar. In particular, the alkyl substituents will contain from eight to 56 carbon atoms with no alkyl substituent containing more than five carbon atoms more or less than any other alkyl substituent. In the most preferred case, the alkyl substituents are tertiary alkyl groups of from 12 to 24 carbon atoms, with all alkyl substituents in a given case having an identical number of carbon atoms.

ilnited States atet 11 1 1111 3,767,577

0gg Oct. 23, 1973 SYNTHETIC LUBE STOCKS [75] Inventor: Jesse K. Boggs, Seabrook, Tex. Exami"e'Herbert Levme Attorney-Thomas B. McCulloch et al. [73] Assignee: Esso Research and Engineering Company, L1nden, NJ. [57] ABSTRACT [22] Flled: 1971 The present invention relates to synthetic lubricant [21] Appl. No.: 171,659 base oil stocks having a low pour point and consisting essentially of an admixture of monoand dialkyl benzenes, wherein the alkyl substituents are substantially if 252/59 fg similar. In particular, the alkyl substituents will con- 19 '2 tain from eight to 56 carbon atoms with no alkyl sub- 1 0 can 2 l5 stituent containing more than five carbon atoms more 7 668 or less than any other alkyl substituent. In the most preferred case, the alkyl substituents are tertiary alkyl [56] References Cited groups of from 12 to 24 carbon atoms, with all alkyl UNITED STATES PATENTS substituents in a given case having an identical num- 3,538,l78 11/1970 Sias 260/671 G ber of carbon atoms. 3,173,965 3/1965 Pappas et al 260/667 3,092,981 6/1963 Begeman et al. 62/114 5 Clalms, 1 Drawing Pour Depressuni Effect of Di in Mono- Teriiury Alkylbenzenes l l l l Pour Poini F. J,

Mole Fraction Di-Teriiary Alkylbenzene SYNTHETIC LUBE STOCKS CROSS-REFERENCE TO RELATED APPLICATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to lubricating oils of lower pour points than would be normally expected. It is more particularly related to blends of alkyl benzenes which can be used as synthetic lubricants and which have low pour points. In its most specific aspects, it relates to a mixture of tertiary alkyl benzenes which have one or two tertiary alkyl groups on the benzene nucleus.

2. Description of the Prior Art Pour point reduction by the blending of dissimilar materials is quite old in the art. In fact, it is normally expected that the admixture of dissimilar materials will result in a reduction of the pour point. However, this reduction in pour point usually follows a more or less straight line relationship where quite small quantities of one material are added to the other, with only a slight depression in the pour point resulting. It has been found by the present inventor that by matching closely the alkyl substituents on monoand dialkyl benzenes, the dialkyl benzene has a strikingly greater pour point reducing effect than would be expected.

DISCUSSION OF THE INVENTION The reduction of pour point is desirable in order to provide good low temperature lubricating service. It is particularly desirable to provide lubricating oils which, while effective as lubricants under the high temperature conditions existing in an operating internal combustion engine, will still remain liquid at the low temperatures which prevail at high altitudes and in the northern latitudes. For certain military lubricating requirements (for example, as aircraft turbine oils), the desirability of low pour point oils is obvious, since the aircraft may operate at high altitudes where extremely low temperatures are experienced and may be based at airfields which experience extremely low temperatures.

The present invention is directed to a composition which has a low pour point. In its most specific aspect, it relates to compositions made up of mono-talkylbenzenes and di-t-alkylbenzenes. These t-alkyl substituents are preferred for lubricating service because they are more resistent to thermal and oxidative degradation. Aromatic nuclei having primary or secondary alkyl substituents are subject to thermal and oxidative degradation because they possess at least one benzylic hydrogen atom; that is, a hydrogen atom on the carbon atom which is alpha to the benzene ring. This type of hydrogen atom is vulnerable and under the conditions experienced in lubricating oil service suffer thermal or oxidative degradation leading to polymerization and the formation of sludge. While it is preferable to use benzenes with tertiary-alkyl substituents, it is not absolutely necessary, and a number of primary and secondary alkyl benzenes have been proposed as synthetic lubricant base stocks. The present invention is applicable to these primary and secondary alkyl substituted benzenes as well as to the tertiary alkyl substituted benzenes. However, it is reiterated that the tertiary alkyl benzenes are preferred.

According to the present invention, a synergistic pour point depressing effect is experienced when the alkyl substituents in the monoalkyl benzene are substantially the same as the alkyl substituents in the dialkyl benzene. In those cases where a tertiary alkyl ben-.

zene is used, the chain lengths of the longest groups in the t-alkyl substituent should be essentially the same as the longest chain lengths in the mono-substituted talkylbenzene. It is believed that the similarity of the substituent groups provides an interference with crystal formation which provides the reduction in pour point.

In the most preferred embodiment, the same alkyl substituent will be used in preparation of the monoalkylbenzene as is used in preparation of the dialkyl benzene.

The present invention contemplates a composition which contains from 0.1 to 40 mol percent of a dialkyl benzene and, correspondingly, from 99.9 to 60 mol percent of a monoalkyl benzene, the total percentages, of course, adding up to 100. Preferably, from 0.5 to 20 mol percent of the dialkyl benzene will be employed, with correspondingly from 99.5 to mol percent of the mono-t-alkylbenzene.

The alkyl substituents will contain from eight to 56 carbon atoms and, in order to assure similarity of the substituents, no alkyl substituent should contain more than five carbon atoms more or less than any other alkyl substituent. As above discussed, the use of talkylbenzenes is preferred and in the more preferred embodiment the alkyl substituents would be at least percent t-alkyl, the remainder being secondary and primary alkyl groups.

In the most preferred embodiment, wherein the greatest pour point reduction is obtained, a mono-talkylbenzene provides the base stock and will constitute from 99.5 to mol percent of the mixture, while the di-t-alkylbenzene will constitute from 0.5 to 5 mol percent. I

In order to illustrate the present invention, several examples are hereinafter given. These examples were obtained by the tertiary alkylation of benzene followed by fractionation into numerous cuts. These cuts were then tested and the relative proportions of monoand di-t-alkylbenzene were calculated from the viscosity data on each cut. The pour point was measured andis and is below in Table I along with an identification of the alkyl structure, the mo] percent of monoand dialkyl benzenes and the viscosity in centistokes at F and 210 F. Note that the alkyl structures are referred to in shorthand by the number of carbon atoms in each branch of the alkyl structure which is attached to the tertiary carbon atom. Thus, the first compound has an alkyl structure of and is i'eferr ed to as (3-1-5). The other structures are similarly identified. Thisreference is used to simplify the later discussion.

TABLE I Pour Point Depression-Alkylbenzenes M01 percent l Poitr Visc., cs. at-

Ex. Alkyl structure Mono- Di- F. 100 F. 210 F.

l CH3 100 ---35 3.93 1.25 I 97. 1 2. 9 55 4. 17 1. 26 CaH1-CC5H11 56. 1 43. 9 35 10.01 2. 04 I 3. 96 5 +5 53. 12 5, 15 0 100 0 56. 60 5. 33

2 CH: 100 0 25 4. 42 1. 31 I 95. 3 4. 7 50 5. 82 1. 65 C4Ha-C-C4Hv 13. 3 86. 7 5 50. 89 4. 86 I 10. 1 89. 9 25 43. 70 5. 37 8. 5 91. 5 -10 56. 58 4. 92 (4-1-4) 0 100 +13 65. 87 5. 63

8 CH: 100 0 40 3.35 1.26 I 96. 5 3. 5 85 3. 45 1. 27 CH3CC1H|5 79.7 20.3 -55 6.16 1.93 I 6. 8 93. 2 35 20. 05 3. 58 0 100 7 21. 96 3. 80

4 CH: 100 O 40 5.41 1.65 I 99. 4 0. 6 70 5. 52 1. 67 CzHs-C-CsHn 97. 1 2. 9 -60 5. 82 1. 71 I 69. 5 30. 5 -50 12. 98 2. 82 15. 1 84. 9 20 37. 57 5. 25 (218) 0 100 19 45. 45 5. 83

1 Calculated from viscosity data.

Referring now to fable i, Example 1 shows the use of the 3-1-5 alkyl structure and it is seen that at 100 percent mono-(3-l-5)-benzene the pour point is 35 F., while at 100 percent di-(3-l-5)-benzene, the pour point is 0 F. When only 2.9 mol percent of the di-alkyl benzene is added, however, the pour point is reduced to 55 F. Similarly, in Example 2 the 4-1-4 substituent is seen to have a low pour point minimum of 50 F. when it contains 4.7 percent di-(4-l-4 )-benzene.

in Example 3 the lowest pour point of --85 F. is seen at about 3.5 mol percent di-(l-l-7)-benzene, and in Example 4 the minimum pour point is seen to be -70 F. with the inclusion of only 6 mol percent of the di-(2- 1-8 )-benzene.

From the above table it can be seen that striking reductions in pour point can be obtained with only very small quantities of the dialkyl benzene. That this is more than would be normally expected can be seen by reference to the drawing wherein the actual minimum pour points are plotted against the expected pour points which were calculated on the theoretical basis that the maximum melting point lowering would be obtained by an equimolar admixture of the monoand dialkyl benzenes. It is obvious from the drawing that the reduction in pour point is substantially lower than that which would be expected. It is to be noted that in the drawing the symbol tb stands for the benzene nucleus.

Having disclosed the essence of my invention, what is to be covered by Letters Patent should be measured not by the disclosure herein given but by the appended claims.

I claim:

1. A synthetic lubricant base oil having a synergistically low pour point, consisting essentially of a. from 0.5 to 5 mol percent of a di-tertiary alkyl benzene, and

b. from 99.5 to 95.0 mol percent of a mono-tertiary alkyl benzene, wherein the alkyl substituents are identical and contain from eight to 56 carbon atoms.

2. A composition in accordance with claim 1 which contains about 2.9 mol percent of and about 97.1 mol percent of 3. A composition in accordance with claim 1 which contains about 4.7 mol percent of K -WQ and abou f9 5 3 ind] ercent of 4. A composition in accordance with claim 1 which contains about 3.5 mol percent of andjcorrespondingly, from about 99.410 about 97.1 mol percent of wanb-cmmQ. 

2. A composition in accordance with claim 1 which contains about 2.9 mol percent of
 3. A composition in accordance with claim 1 which contains about 4.7 mol percent of
 4. A composition in accordance with claim 1 which contains about 3.5 mol percent of
 5. A composition in accordance with claim 1 which contains from about 0.6 to about 2.9 mol percent of 